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7143885 
Journal Article 
Effects of rare-earth elements and alkali metals on the superconductivity of (Tl0.7M0.3)Sr2Ca0.8Cr0.2Cu2O7 with M = Gd, Er, La, Li, Na, K, and Rb 
Abu Bakar, IP; Abd-Shukor, R; , 
2019 
Yes 
Journal of Alloys and Compounds
ISSN: 0925-8388 
ELSEVIER SCIENCE SA 
LAUSANNE 
745-750 
WOS:000449651100089 
The effects of rare-earth elements M = Gd, Er, and La and alkali metals M = K, Li, Na, and Rb substitutions on Tl0.7M0.3Sr2Ca0.8Cr0.2Cu2O7 (Tl-1212) were investigated. The characterization includes X-ray diffraction method, scanning electron microscopy, electrical resistance and AC susceptibility measurements. Xray diffraction patterns showed that almost all samples consisted of major Tl-1212 and minor Tl-1201 and Ca0.3Sr0.7CuO2 phase. Rare-earth elemental substitution improved the formation of the Tl-1212 phase but suppressed the transition temperature. Scanning electron micrographs showed smaller grain size in the substituted samples compared with non-substituted sample. The temperature-dependent electrical resistance measurements showed metallic normal state behavior for all samples. Alkali metals substitutions showed higher zero transition temperature, Tc-zero compared with the rare-earth elemental substitution. AC susceptibility measurements showed a higher superconducting transition, T-c chi' for alkali metals substitutions (84-93 K) compared with the rare-earth elemental substitutions (50-61 K). The inter-grain critical current density at the peak temperature T-p of the imaginary part chi", J(c)(T-p) measured using the Bean's model was between 17 and 22 A cm(-2). The effects of rare-earth elements and alkali metals substitutions were discussed in terms of ionic radius and the concept of average Cu valence. (C) 2018 Elsevier B.V. All rights reserved.